The present invention relates to the rotor blades of a turbomachine, such as a gas or steam turbine or the like. More specifically, the present invention relates to a method and apparatus for determining the amount and type of permanent deformation that such blades experience as a result of operation.
A turbomachine typically comprises a centrally disposed rotor rotating within a stationary cylinder. A large number of blades are attached at the periphery of the rotor and are arranged in circumferentially extending rows. As a result of the high stress levels experienced by the blades--caused by centrifugal force, gas bending loads and differential thermal expansion--combined with the high temperatures to which they are subjected, turbomachine blades sometimes experience permanent deformation due to creep, especially after long operating times, or due to frictional contact between the surfaces of adjacent blade shrouds. Permanent deformation may also be caused by contact, such as contact with other blades in the row in the case of shrouded blades, contact with the cylinder or the adjacent rows of stationary vanes or with foreign objects.
Quantifying the type and amount of deformation can help one to determine the cause of the deformation, as well as whether the blade can safely be returned to service for continued operation. Unfortunately, due to the complex shape of modern high performance blades and the complex stress patterns to which they are subjected, the deformation may assume a complex configuration. Consequently, it is extremely difficult to quantify and categorize blade deformation. This difficulty is exacerbated by the fact that removal of the blades from the rotor is a time consuming process. Thus, it is preferable to be able to check for blade deformation without removing blades from the rotor.
It is therefore desirable to provide a method and apparatus for determining, in situ, the amount and type of deformation a turbomachine blade has undergone. It would also be desirable to check blade radial position during assembly and after any subsequent manufacturing operation.